Snow Load Seismic Weight

[DCBII]

ASCE 7 says to use 20% of any snow load greater than 30psf as seismic weight. This causes a problem for the 0.6D+0.7E load combination. The snow load acts as seismic weight, but does not resist uplift and overturning. Can't the 20% be used to resist uplift and overturning if it's included as seismic weight?

 

[MiketheEngineer]

I would say: probably - but it also says only 2/3 or .60 of dead loads can be used. But since it really is a live load - I would use it.

But you need to check everything without any snow, also.

 

[ishvaaag]

This is a question more for the ASCE regulators or whomever has to approve some particular use of it.

It is clear snow can be out of sync with roof when an earthquake strikes but what we really are in lack of is in knowing how complete have been the investigations and calibrations to decide that some combinations represent the economically targeted safe structural limit to the behaviour that is also so consistent as to no permit to use the snow that is the loading as inertial mass; it is not neccesarily so, but I frankly doubt verily much the purported consistence of the codes we are one way or another being enforced to comply stands as stated and produce such homogeneously reliable structures as to require the tight-to the line interpretations of the same. Even the vertiginous changes in the codes must be showing that is the case.

 

[hawkaz]

I would use the 20% to resist the overturning and uplift. As you stated, if the load is in place to cause the seismic load increase, then it is also in place to help resist the loads.

I use this same logic with storage live loads

 

[rowingengineer]

I wouldn't use the snow weight, snow moves to much for my liking.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”

 

[ishvaaag]

rowingengineer, much? how do you have reached to such conclusion?

http://www.youtube.com/watch?v=YaRM44sh0TY&feature=player_embedded

Heh.

 

[ishvaaag]

Hmm I see there have been victims, sorry for that.

 

[SteelPE]

I've always applied the load to the structure how the code tells me to. This means that I include the 20% of snow load in the seismic calculations, however, I do not count on any of the snow load to counteract the overturning or uplift cases. Some people may do it differently, I just follow the code.

For large buildings in with large snow loads, this can add a considerable amount of load to the LFRS.

 

[MiketheEngineer]

Maybe that is why we are Professional Engineers......

Sometimes we have to make our own decisions based on education and experience...

Don't most state boards have some wording along those lines...

 

[rowingengineer]

ishvaaag,
Well it is just a logic thing for me, when building moves the snow is able to move. As such how can you determine if the snow is near the centre or outside of the building for over-turning and uplift. I should clarify this with the fact that I live in a tropical region that only see's snow on TV, as such I don't really have much knowledge of snow.



ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”